This invention relates generally to an imaging system, and more particularly, to calibration of a medical imaging system.
In at least some known imaging systems, a radiation source projects a cone-shaped beam which passes through the object being imaged, such as a patient and impinges upon a rectangular array of radiation detectors. In some known tomosynthesis systems, the radiation source rotates with a gantry around a pivot point, and views of the object are acquired for different projection angles. As used herein xe2x80x9cviewxe2x80x9d refers to a single projection image or, more particularly, xe2x80x9cviewxe2x80x9d refers to a single projection radiograph which forms a projection image. Also, as used herein, a single reconstructed (cross-sectional) image, representative of the structures within the imaged object at a fixed height above the detector, is referred to as a xe2x80x9cslicexe2x80x9d. And a collection (or plurality) of views is referred to as a xe2x80x9cprojection dataset.xe2x80x9d A collection of (or a plurality of) slices for all heights is referred to as a xe2x80x9cthree-dimensional dataset representative of the image object.
One known method of reconstructing a three-dimensional dataset representative of the imaged object is known in the art as simple backprojection, or shift-and-add. Simple backprojection backprojects each view across the imaged volume, and averages the backprojected views. A xe2x80x9cslicexe2x80x9d of the reconstructed dataset includes the average of the backprojected images for some considered height above the detector. Each slice is representative of the structures of the imaged object at the considered height, and the collection of these slices for different heights, constitutes a three-dimensional dataset representative of the imaged object. Alternatively, in a two-dimensional scan, such as, for example, a Cranio-caudal scan (CC scan) or a mediolateral-oblique scan (MLO), only a single slice is acquired constituting a two-dimensional dataset representative of the imaged object.
Uniformity between individual detector elements is important for securing good image quality of mammography images. Otherwise, anomalies may occur in the collected data. A consequence of data anomalies is image distortions, commonly referred to as artifacts. Detector uniformity may be impacted by many factors which include, but are not limited to, radiation damage, moisture damage, electromagnetic fields, and sensitivity of the scintillator materials. To correct for this uniformity, periodic calibrations of the detector are required.
In at least one known method of calibration, a reference set of measurements of known glandular and fatty tissue composition is required. Collecting this set of reference measurements may require multiple scans of the object being imaged.
A calibration phantom system for use with an imaging system is provided. The calibration phantom system includes a first phantom element material block having a first surface at a first height, wherein the first phantom element material block at least partially includes a first material having a first attenuation coefficient. The calibration phantom system also includes a second phantom element material block having a second surface at a second height different than the first height, the second phantom element material block at least partially includes a second material having a second attenuation coefficient different than the first attenuation coefficient, wherein the first phantom element material block and the second phantom element material block are co-positioned on a detector.
A method for calibration of an imaging system including a radiation source and a digital detector is provided. The method includes providing a calibration phantom system including a first phantom element material block having a first surface at a first height, wherein the first phantom element material block at least partially includes a first material having a first attenuation coefficient. Providing a calibration phantom system also includes providing a second phantom element material block having a second surface at a second height different than the first height, the second phantom element material block at least partially including a second material having a second attenuation coefficient different than the first attenuation coefficient, wherein the first phantom element material block and the second phantom element material block are co-positioned on a detector. The method also includes imaging the calibration phantom system to obtain phantom images, processing the phantom images, and extracting a plurality of calibration values from the processed phantom images.
A computer readable medium encoded with a program executable by a computer for calibration of an imaging system including a radiation source and a digital detector is provided. The program is configured to instruct the computer to image the calibration phantom system, wherein the calibration phantom system includes a first phantom element material block having a first surface at a first height, wherein the first phantom element material block at least partially includes a first material having a first attenuation coefficient. The calibration phantom system also includes a second phantom element material block having a second surface at a second height different than the first height, the second phantom element material block at least partially including a second material having a second attenuation coefficient different than the first attenuation coefficient, wherein the first phantom element material block and the second phantom element material block are co-positioned on the detector. The program is also configured to instruct the computer to obtain phantom images, process the phantom images, and extract a plurality of calibration values from the processed phantom images.